1. Field of the Invention
This invention relates to telephony digital signal transmission, and more particularly to a method of boundary discrimination of a frame signal which defines the starting point of data to be transmitted or received.
2. Description of Related Art
Digital telephone circuits carry signals within predetermined time periods known as frames delineated by an 8 KHz timing signal or clock known as a frame pulse, which establishes a frame boundary. Each frame therefore defines a 125 microsecond period in which a digitized voice signal may be processed.
Different telephone circuits often have to be synchronized with each other for correct interoperation. In such synchronous systems, higher speed timing signals, which are synchronous to the 8 kHz timing signal, are also employed. These high speed timing signals are used to clock state machines that process signals. A state machine in effect maps an ordered sequence of input events into a corresponding sequence of output events. The capacity of related state machines to process signals in such a system is limited by the number of clock cycles available in a 125 microsecond frame.
This constraint may be reduced by increasing the frequency of the clock available to each individual circuit in the system, but the usage of higher speed clocks has the drawback of increasing the sensitivity of system to clock skew between components as well as increasing the level of electromagnetic radiation emanating from the clock tracking on the circuit board.